Interpretive Summary: Developing knowledge of exotic or emerging virus diseases of corn before they become epidemic in the U.S. allows researchers to devise disease control strategies for the corn seed industry and producers and ease the economical loss from the disease. We found a new virus in corn samples collected from Arizona. Symptoms similar to those produced by this new virus were observed in field corn by researchers in Arizona and California. However, these researchers were unable to maintain the virus under experimental condition, limiting their ability to study the disease. Based on vascular puncture inoculation technology we developed, we have transmitted and maintained the virus in culture. We characterized the new virus and developed an antiserum and serological assay for the virus. Researchers, extension specialists and producers can now confirm the identity of this new virus, maize necrotic streak virus, using the serological assay.

Technical Abstract:
A new maize virus was isolated from maize leaves from Arizona showing mild mosaic symptoms and co-infected with maize dwarf mosaic virus (MDMV). The virus is readily transmitted by vascular puncture inoculation (VPI), but not by leaf rub inoculation. Virus symptoms on susceptible maize include pale green or yellow to cream color spots and streaks, measuring 1-2 mm on the first emerging leaf at 5-7 days after VPI. As the leaves developed and expanded, the spots and streaks became spindle-shaped, then coalesced into long chlorotic bands. These bands became translucent and necrotic around the edges. There was a distinctive chlorosis on the stalks that also became necrotic. Neither Aphis maidis-radicus, Myzus persicae, Macrosiphum euphorbiae, Rhopalosiphum padi, Schiaphis graminum, Dalbulus maidis, Graminella nigrifrons, Perigrinus maidis nor Diabrotica virgifera virgifera transmitted the virus under persistent or non-persistent conditions. Maize germ plasm showed both susceptibility and resistance to virus infection. Extract from infected plants contained many virions. Electron microscopic and SDS-PAGE analyses of purified virus fractions indicated the virus consisted of isometric particles (32 nm diameter) and a putative 28 kDa coat protein band. The viral genome was composed of an abundant 4.3 kb single-stranded RNA. The virus tested negative in F(ab')2 ELISA for MDMV, maize chlorotic dwarf, maize stripe and maize white line mosaic viruses. Based on its distinctive symptoms, the new virus was conditionally named maize necrotic streak virus.